The present invention relates to a device, method and control for extracting dew from ambient atmosphere.
Water is present in the ambient atmosphere in the form of moisture and this moisture will condense into droplets onto a surface (dew) when the surface is at or below a certain temperature (based upon relative humidity) referred to as the dew point. As the moisture condenses as dew, it releases a latent heat, that is, it releases energy without a change in temperature. This latent heat, however, must be dissipated or removed or it will cause the surface temperature to rise until it is above the dew point and droplets will no longer form. Further, the excess latent heat could also cause droplets that have already formed to evaporate back into atmospheric moisture.
Devices for extracting water from the atmosphere by cooling a surface to below the dew point are known. For example, such a device is described in applicant's earlier patent, U.S. Pat. No. 4,315,599, the disclosure of which is incorporated herein in its entirety. In that patent, a device, such as a Peltier device is used to continuously cool a surface below dew point to form a collection surface for condensed water droplets. Those condensed droplets are then harvested and utilized.
Other devices, such as air conditioning units include a coil through which a refrigerant flows which has been chilled to a temperature below dew point. Typically a compressor is used to compress the refrigerant, from a gas to a liquid, and then the liquid flows through an evaporator where the temperature of the refrigerant drops as the refrigerant changes state from a liquid to a gas, thereby lowering the temperature of the coil. As air flows over the chilled coil, moisture in the air will condense on the coil. The latent heat released from the water moisture as the moisture condenses into droplets is transferred primarily to the refrigerant which must be cooled again, usually in a condenser to in order for additional moisture to be condensed from the air.
In many parts of the world, fresh liquid water is in short supply, even though there is considerable water available in the atmosphere in such regions. However, the costs involved in running a compressor continuously to dissipate the latent heat released from the moisture as it condenses into droplets are very high and the size and costs of the compressors needed for operating on such a continuous manner are quite large, rendering the possibility of using such systems for obtaining usable amounts of fresh liquid water rather low.
Consequently, it can be seen that the need exists for a system that can extract water from the atmosphere, such as in the form of dew, in reasonable quantities at reasonable costs.